Connecting rods are needed for all sizes and types of engines. A typical engine connecting rod 10, shown in FIG. 1, has an apertured large end encompassing a crank bore 20 adapted for installation about a crankshaft journal. The smaller apertured end encompassing a pin bore 24 is connected to the piston assembly to transfer power from the engine to the drive train. The shank 26 connects the two ends.
In the past, connecting rods were manufactured from solid steel blanks. Grinding and boring operations fashioned the blank to the desired specifications. More recently, powder metal has been used to more accurately and efficiently create preformed connecting rod blanks that are then subjected to standard grinding and boring operations. A brief explanation of the prior art manufacturing operation is as follows with reference to FIG. 1:
In the prior art connecting rod manufacturing process, a preformed metal connecting rod blank is obtained (see generally FIG. 1), although, today many of the preformed metal connecting rod blanks are made of powder metal. Regardless, the connecting rod blank is already manufactured to general connecting rod specifications, including having preformed features such as crank, pin holes, and bolt holes. The connecting rod blank is then machined to the required specifications.
In the prior art, the connecting rod blank is placed in a station-to-station manufacturing line to machine the part to the required specifications. First, in Station #1, the thickness of the component is rough-ground. Then the part is transferred to Station #2 where a rough bore process more accurately defines the bore requirements and where fracture notches 32 are formed on the large aperture end portion. While each operation is typically performed on numerous, dedicated and separate machines, this step is generally designated as Station #2.
The part is then transferred to Station #3 where the cap 22 is fracture split along the fracture notches 32 to crack the rod into two parts across the large aperture end portion. The connecting rod may then be assembled to ensure proper mating. A final finish grind is performed at Station #4 to ensure appropriate thickness of the connecting rod. A final finish bore is then performed at Station #5 to ensure appropriate bore sizes. Finally, the entire component is honed with abrasive tools to ensure appropriate smoothness and mating surface requirements at Station #6. Significantly, the machines required at each of the aforementioned Stations are well-known to those skilled in the art.
The connecting rod manufacturing art is constantly looking for ways to make the manufacture of connecting rods faster, cheaper, and easier. Because large numbers of parts are manufactured each year according to the above-identified manufacturing process, any efficiency in manufacture can result in substantial cost and time savings. For example, U.S. Pat. No. 5,946,790 (incorporated by reference herein) teaches a process for mass producing connecting rods by way of a station-to-station assembly line production method and apparatus.
While connecting rods have been manufactured for decades, relatively recent improvements in engine designs require such connecting rods to be manufactured to highly specific tolerances and dimensions. These highly specific dimensions and tolerances render many of the previously known methods of manufacturing connecting rods either inefficient or obsolete.
The use of fracture splitting in connecting rods has also been known in the art for many years. However, as discussed in U.S. Pat. No. 4,198,879 (incorporated by reference herein), failure rates for fracture splitting techniques have approached 40% in some previously known methods. Moreover, many of the previously known methods did not provide for a means of consistently and efficiently mass producing connecting rods having the necessary tolerances and dimensions, such that additional boring, grinding and honing (as mentioned above) was often needed, thereby resulting in added costs in terms of machinery and spatial requirements along the manufacturing line itself.